The unwitting use of fog lamps, and more particularly the rear fog lamps which are intended for giving an indication to the drivers of following vehicles of the presence of the vehicle in which the rear fog lamps are installed, is dangerous to the drivers of those following vehicles when illumination of the rear fog lamps is not justified. The drivers of the following vehicles can be dazzled under these circumstances, and may be unable to distinguish quickly enough when, for example, the brake lights of the vehicle in front of them light up to show that the brakes are being applied. This can cause collisions.